Short answer
A counterfeit Rolex GMT-Master II "Batman" fails on four points that are cheap to check: the ceramic bezel insert, the cyclops magnifier, the bracelet end links, and the movement under a loupe. The real watch carries a blue and black Cerachrom insert with platinum-coated numerals, a 2.5x date magnifier, solid end links that meet the case with a constant hairline gap, and a Rolex calibre 3186 or 3285 with a free-sprung balance. Fakes get the color split, the printing, or the finishing wrong on at least one of those four.
What the "Batman" actually is
The nickname covers the GMT-Master II with a blue and black 24-hour bezel. Reference 116710BLNR arrived in 2013 on an Oyster bracelet with the calibre 3186. Reference 126710BLNR replaced it in 2019 with the calibre 3285, a 70-hour power reserve, and a choice of Oyster or Jubilee bracelet. Collectors call the Jubilee version the "Batgirl." A seller who mixes those details, for example advertising a 2013 case with a Jubilee bracelet and a 70-hour movement, is describing a watch that never left the factory.
What you need before you look
A 10x jeweler's loupe, a bright LED light, and a phone that shoots macro. Calipers help if you can measure case thickness. Ask for natural-light photos of the dial, the clasp, and both sides of the case back before you meet anyone.
Step-by-step inspection
- Read the bezel insert through the loupe. Genuine Cerachrom is matte blue fused with black, and the 24-hour numerals sit in a thin platinum layer with visible texture. Fakes use painted or stickered metal that looks glossy and shows printing dots at the edges of the numerals.
- Check the color split. On a genuine insert the blue and black halves divide at the 6 and 18 hour positions. On fakes the split drifts, and the blue reads purple in daylight.
- Inspect the cyclops. The genuine 2.5x lens shows almost no rim distortion and the date sits in the center of the aperture. Fakes produce a warped date, ghosting on the numerals, or a blue anti-reflective bloom.
- Look at the dial text. Rolex prints "GMT-MASTER II" in a crisp serif with even stroke weight. Fakes show blobby letters, uneven spacing between lines, or a crown logo with missing dots.
- Study the hands and hour markers. White gold surrounds on genuine markers have a mirror edge. Fakes use painted rims or rhodium that turns grey.
- Turn the bezel. A genuine bezel rotates through 24 firm clicks with no side play. A fake feels loose, gritty, or spins with a plastic click.
- Measure the bracelet and end links. Genuine solid end links meet the case with a hairline gap that stays constant. Fakes show a wide gap under one lug, sharp unfinished edges, or a clasp that rattles.
- Test the crown and winding. Screw the crown down and count the turns. A genuine GMT crown takes about two and a half smooth turns. A fake often stops after one turn or cross-threads.
- Check the movement with a loupe or phone macro. The genuine calibre 3285 has a blue Paraflex hairspring, Geneva stripes with clean bevels, and a rotor that spins without scraping. Copy movements, from an ETA clone to an unbranded automatic, show rough grinding, painted rotor text, and a balance running at 21,600 vph instead of 28,800.
- Weigh the watch. A genuine 126710BLNR on a full bracelet lands near 155 grams. Most fakes sit between 120 and 140 grams because the steel is thinner and the case back is hollow.
Paperwork and price reality
Boxes, hang tags, and cards are easy to copy, so they prove nothing. What matters is the reference number stamped between the lugs, the serial, and whether those two match any service record. A Batman trades well above retail on the secondary market, so a price at a fraction of that number is the strongest single signal. No seller who owns a real one discounts it by half.
When you still cannot tell
Take the watch to a Rolex-authorized service center or an independent watchmaker with Rolex parts access. Removing the case back takes minutes and settles the movement question. Any seller who refuses that step is telling you what you need to know.